PURPOSE: To enable test printing to be started in a single storke, by a construction wherein a means for turning ON and OFF a power source in the condition in which a feeding terminal is grounded by turning ON a switch is provided at a feeding terminal and power source input part of a controlling part for a thermal- type printer.

CONSTITUTION: When a spring-back button switch SW3 is depressed to turn ON and OFF a contact, a point (a) is grounded. This condition is inputted into a monostable multivibrator 4 with a delay set by a delay circuit 3, and a pulse for grounding the feeding terminal is generated by the monostable multivibrator 4. On the other hand, the condition is inputted into a monostable multivibrator 6 with a delay set by a delay circuit 5, and a high-level pulse is generated by the monostable multivibrator 6. The pulse is inputted into a driving circuit 7, and a relay RL is operated over a high-level period. During this operation, a contact r1 is turned OFF. Namely, simply by depressing the switch SW3, a power source of +5V is turned OFF and ON during when the feeding terminal is grounded, whereby test printing is started.